A truck equipped with one or more auxiliary hydraulic units conventionally employs a main hydraulic pump which may be driven from a power takeoff or is connected to a vehicle crankshaft either directly or via belts and pulleys. Each auxiliary unit conventionally is coupled to the main pump by hydraulic lines through which pressure fluid is circulated continuously if the main pump operates continuously, or to a hydraulic motor that communicates with the main pump. It thus has been necessary to include in conventional systems complex valve, flow divider, or clutch arrangements to enable an operator to assert effective control over the operation of the main pump and the auxiliary units operated thereby.
Among the objects of the present invention is to provide a pump system which minimizes the complexities of known constructions.